Whether dealing with liquids, solids, gases, or any combination of these phases, the fundamental object to be accomplished by mixing is always the same, namely, to achieve uniformity, i.e., to place each particle of any one material as nearly adjacent as possible to a particle of each of the other materials present. In practice, these results are never obtained and to date there has not been developed any formula or equation that can be used to calculate degree or speed of mixing under a given set of conditions in order to achieve this fundamental objective.
Because of the fact that the mixing art is so empirical, and the almost infinite variety of substances to be mixed, each industry has developed mixing equipment particularly for its own use. Such diversification in mixing equipment is not only unnecessary, but it is the greatest obstacle to sound coordination of knowledge in the mixing art.
In many chemical operations it is desirable to uniformly intermix one material with another within a controlled period of time. In order to achieve this it is advantageous to introduce the added material at or near the point where the most significant mixing action occurs. U.S. Pat. Nos. 146,339; 335,574; and 3,725,193 have suggested controlling the point of addition of one material with another by introducing material through a central stirring member.
Problems known to exist with present mixing equipment include (a) the difficulty of keeping apparatus clean and particularly keeping openings in the stirring members from becoming clogged, (b) the difficulty and time required to remove stirring members having fixed vanes, i.e., extended arms, from mixing containers, (c) the necessity in many cases of conducting mixing operations in equipment designed solely for that purpose, (d) the problem of the substantial initial torque required when attempting to rotate a mixing bar with fixed arms in a dense solid mixture or in material which has a high degree of compaction, (e) the necessity of using different equipment to accomplish gentle agitation, for solids-solids blending, for liquid-solids mixing and for introducing gases into liquids, and (f) the difficulty of regulating the amount and timing of material introduced via a central stirring member.
With the requirement in various industries, such as the pharmaceutical industry and food industry, for mixing materials under conditions which avoid opening a container and exposing its contents to the environment and the necessity in other industries to avoid exposing individuals to the contents of poisonous or otherwise hazardous material, there has been an increasing awareness of the need for improved mixing equipment which can be utilized under such conditions.